Mercury emissions from various industries has become a serious environmental issue. The largest sources of mercury emissions in the US are utility boilers, followed by waste incinerators that combust mercury-containing wastes (municipal and medical), coal-fired industrial boilers, and cement kilns that combust coal-fired fuels. Other potentially important sources of mercury emissions are manufacturing plants and basic chemical processes. One particularly notable source of mercury emissions is coal-fired power plants. These plants emit large amounts of mercury each year, and will be required to reduce their emissions level by greater than 90% by 2010. Consequently, mercury is listed by the International Program of Chemical Safety as one of the most dangerous chemicals in the environment.
Vapor phase mercury settles over waterways, polluting rivers and lakes, and contaminating fish. Further, exposure to mercury poses real risks to public health, especially to children and developing fetuses. Exposure to mercury has been associated with both neurological and developmental damage in humans. The developing fetus is the most sensitive to mercury's effects, which include damage to nervous system development. People are exposed to mercury primarily through eating fish that have been contaminated when mercury from power plants and other sources is deposited to water bodies. Once mercury enters water, biological processes can transform it into methylmercury, a highly toxic form of mercury that builds up in animal and human tissues. In fact, methylmercury can accumulate in some fish in concentrations thousands of times higher than in the waters they live in, which is why state environmental regulatory agencies often issue fish-consumption advisories. As previously mentioned, the greatest source of mercury emissions is power plants, and historically they have not been required to control these emissions until recently.
As part of the Clean Air Mercury Rule (CAMR), power plants will soon be required to measure mercury emissions on a continuous basis. There are three forms of mercury in stack (flue) gas from a coal-fired power plant that can potentially be monitored by a mercury monitoring system, namely Hg0, oxidized Hg+2, and particulate bound Hg of either species, at stack gas temperatures in excess of 200° F. However, the Environmental Protection Agency (EPA) does not currently require the continuous monitoring of particulate bound Hg0. Accordingly, total mercury for monitoring in accordance with EPA regulations, i.e. gaseous mercury is the sum of elemental mercury (Hg0) and oxidized mercury (Hg++). One leading method of measuring mercury emissions on a continuous basis is to capture the mercury in a bed of sorbent (40 CFR, Part 75), following the procedures outlined in Appendix K of the CAMR. Appendix K is a set of protocols and stated criteria that must be met to in order for the U.S Environmental Protection Agency (EPA) to consider the method valid. While continuous emissions monitoring is required for mercury testing from a stack gas there is also a requirement for a backup system using dual sorbent traps.
Samples of stack gas are usually taken by inserting a probe into the stack at a predetermined location and for a predetermined length of time to complete a test cycle. The probe can be one wherein stack gas is continuously conducted through the probe to an analytical device designed to measure mercury. The analytical device can be either in the proximity of the probe or at ground location. The probe can also be one that contains a sorbent trap at its tip extending into the stack so that as stack gas is conducted through the probe mercury is captured on the sorbent in the trap. The flue gas sample is then dried and expelled into the atmosphere. If sorbent traps are used the probe will be removed from the stack and the sorbent traps removed for analytical testing at the end of a test cycle. Fresh sorbent traps are then inserted in the probe and the probe reinserted in the stack for further sampling.
There are several disadvantages associated with the use of conventional sorbent trap/probe equipment. For example, the probe which typically weights about 100 lbs is generally inserted into a stack several hundred feet off the ground. Thus, it is often difficult and cumbersome for a technician working on a narrow platform several hundred feet off the ground to remove the probe and safely change-out the sorbent traps. There is always the danger that the sorbent traps, which typically extend past the end of the probe will be broken in event the probe inadvertently hits an object while the probe is being inserted or removed from the stack. Therefore there is a need in the art for improved equipment and techniques that lessen the danger of damage to the sorbent traps during insertion and removal of a probe, containing one or more sorbent traps, from a stack.